Continuous halftoning using quarternary pixel cells

Details Continuous halftoning using quarternary pixel cells Continuous halftoning using quarternary pixel cells

1989-06-09

1990-10-16

Reynolds, Bruce A.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358458, H04N 123

Patent

active

049639900

ABSTRACT:
A method of obtaining continuous tone reproductions in a raster scanned digital image having a given number of pixels for each halftone cell of the digital image and using four modulating levels for each pixel of the output scanner including a black and a white pixel level, the method comprising the steps of: choosing two reflectance gray levels intermediate the black and white levels to combine with the black and white pixel levels for providing quadruples, four numbers specifying the number of each kind of pixel in the halftone cell, for modulating the output scanner, determining a total number of average halftone cell gray levels to be available for the digital image, creating a list of quadruples that describe all possible average halftone cell grey levels available with the four modulating levels, and selecting a set of quadruplets from said list equal to a desired number of gray levels, said set of quadruplets selected to maximize the occurrence of black and white pixel levels in each halftone cell.

REFERENCES:
patent: 4078929 (1978-03-01), Gundlach
patent: 4434431 (1984-02-01), Ohkubo et al.
patent: 4491875 (1985-01-01), Kawamura
patent: 4651287 (1987-03-01), Tsao
patent: 4692773 (1987-09-01), Saito et al.
patent: 4714964 (1987-12-01), Sasaki

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